It is known to provide industrial trucks and other vehicles with an electrical steering system. The rotation of a steering transmitter is measured with the help of a rotation angle sensor and the rotation angle signal is given to an actuator, which depending on the measured rotation angle creates a steering angle for a wheel to be steered. For these types of electrical steering systems as well as for other applications, the security in the angle capture is of importance. A failure of the electrical steering system or a wrong angle display can have uncomfortable consequences if not detected in a timely manner.
It is known to determine a rotation angle with the help of an electrical potentiometer. It is also known to determine an angle of rotation in that two magnetic field sensitive orthogonally arranged sensor elements, e.g. hall sensors, work together with one permanent magnet, which is e.g. arranged on the shaft of the steering transmitter. The sensor elements create sinusoidal output signals depending on the rotary motion of the magnet [X=A·cos(Θ)+B und Y=A·sin(Θ)+B]. With the help of a formula saved in an evaluation unit, e.g. Θ=α tan 2(Y−B, X−B), a rotation angle is calculated in a processor and processed further. The rotation angle can be determined relatively exactly with this type of rotation angle sensor. It is disadvantageous that errors, which are caused by the failure of a sensor element, e.g. due to a wire break or the appearance of impermissible drift phenomena, such as static external magnetic fields, are not detected right away under some circumstances.
The object of the invention is to create a rotation angle sensor, in particular for electrical steering systems for industrial trucks, which is monitored for failures.